1. Field of the Invention
The present invention relates in general to the field of information handling system audible noise, and more particularly to a system and method for reduction of information handling system audible noise related to power state transitions.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
As information handling systems have grown in number, the cumulative power consumed by individual systems has become a growing concern. Industry and environmental groups have worked to decrease power consumption by generating and using a number of power conservation steps, such as automated power downs of systems and displays after periods of nonuse. Power conservation initiatives have naturally focused on information handling system components that consume greater amounts of power and especially on components having operational settings with variable power consumption. For example, a common power conservation technique is to throttle the central processing unit (CPU) to a variety of power saving states. The CPU is typically capable of transitioning dynamically between a fully active state and one or more different “sleep” states in a manner that is generally seamless to the user of the system. Throttling of a CPU between a variety of power saving states is particularly attractive with portable information handling systems when operating on an internal battery power source. When a portable system detects an idle state, throttling of the CPU is accomplished with minimal impact on the user of the system, thus increasing the time of the battery life between recharges.
One difficulty that arises from the frequent transition between various CPU power states is that each transition tends to generate audible noise due to the peso-electric effect that accompanies changes in power applied to the CPU. The peso-electric effect results when sudden changes to CPU core voltages change the linear dimensions of ceramic capacitors used to decouple power rails. Changes in the linear dimensions of capacitors translates into board vibrations which are sometimes perceived by a user as a high-pitched audible noise. Typically, transitions between CPU power states occur at regular intervals, usually at 1 mS intervals, so that harmonics from these transitions produce a squealing noise that is annoying to users and sometimes perceived by users as a failing system. One way to minimize the audible noise is to replace the ceramic capacitors with POSCAPS that do not experience the peso-electric effect. However, POSCAPS are typically five times as expensive as ceramic capacitors and a typical CPU power regulator uses four to six of these capacitors. Other alternatives to reduce noise include mechanical modifications to the information handling system housing to reduce noise effects and masking entry into power saving states until a fixed timer expires, however, these techniques generally have an inadequate impact on the noise.